Numerical simulation for predicting concentration profiles of cohesive sediments in surf zone

AbstractA hybrid numerical model is introduced for simulation of cohesive sediments concentration profiles in a surf zone. For this purpose, wave height reduction must be considered, due to muddy beds and wave breaking. Models, such as Sanford and Maa’s erosion model, Krone’s sedimentation model, Tajima’s wave breaking model and the visco-elastic–plastic rheological model, are used to investigate the interaction of wave and bed and to predict the concentration profile. A splitting algorithm has been used to split the three-dimensional advection–diffusion equation into a horizontal, two-dimensional equation, and a vertical, one-dimensional equation, due to different length scales. The one-dimensional equation is discretized over a non uniform grid, and, then solved implicitly using the QUICKEST scheme (third order in time and space). The two-dimensional equation is divided into two parts (advection and diffusion) and each part is separately solved at different time steps. A suitable mesh, regarding space and time intervals, is chosen for considering the stability of the present model. The computational domain extends from the shoreline to the deepwater zone. Finally, the results are analyzed and compared with experimental and field data and other models. Good agreement has been obtained with the data and other numerical models

Numerical simulation for predicting concentration profiles of cohesive sediments in surf zone

A hybrid numerical model is introduced for simulation of cohesive sediments concentration profiles in a surf zone. For this purpose, wave height reduction must be considered, due to muddy beds and wave breaking. Models, such as Sanford and Maa’s erosion model, Krone’s sedimentation model, Tajima’s wave breaking model and the visco-elastic–plastic rheological model, are used to investigate the interaction of wave and bed and to predict the concentration profile. A splitting algorithm has been used to split the three-dimensional advection–diffusion equation into a horizontal, two-dimensional equation, and a vertical, one-dimensional equation, due to different length scales. The one-dimensional equation is discretized over a non uniform grid, and, then solved implicitly using the QUICKEST scheme (third order in time and space). The two-dimensional equation is divided into two parts (advection and diffusion) and each part is separately solved at different time steps. A suitable mesh, regarding space and time intervals, is chosen for considering the stability of the present model. The computational domain extends from the shoreline to the deepwater zone. Finally, the results are analyzed and compared with experimental and field data and other models. Good agreement has been obtained with the data and other numerical models

Lattice Boltzmann solution of advection-dominated mass transport problem:a comparison

Abstract This article addresses the abilities and limitations of the Lattice Boltzmann (LB) method in solving advection-dominated mass transport problems. Several schemes of the LB method, including D2Q4, D2Q5, and D2Q9, were assessed in the simulation of two-dimensional advection-dispersion equations. The concept of Single Relaxation Time (SRT) and Multiple Relaxation Time (MRT) in addition to linear and quadratic Equilibrium Distribution Functions (EDF) were taken into account. The results of LB models were compared to the well-known Finite Difference (FD) solutions, including Explicit Finite Difference (EFD) and Crank-Nicolson (CN) methods. All LB models are more accurate than the aforementioned FD schemes. The results also indicate the high potency of D2Q5 SRT and D2Q9 SRT in describing advection-controlled mass transfer problems. The numerical artificial oscillations are observed when the Grid Peclet Number (GPN) is greater than 10, 25, 20, 25, and 10 regarding D2Q4 SRT, D2Q5 SRT, D2Q5 MRT, D2Q9 SRT and D2Q9 MRT, respectively, while the corresponding GPN values obtained for the EFD and CN methods were 2 and 5, respectively. Finally, a coupled system of groundwater and solute transport equations were solved satisfactorily using several LB models. Considering computational time, all LB models are much faster than CN method

Some numerical aspects of modelling flow around hydraulic structures using incompressible SPH

Here, we apply incompressible smoothed particle hydrodynamics (ISPH) to simulate free-surface flow around hydraulic structures using several classical case studies including dambreak, flow under a submerged gate, and simultaneous operation of a weir and gate. Due to many complexities such as unknown free-surface, rapidly varied flow, trans-critical flow, complicated geometry, and non-hydrostatic pressures, flow fields have traditionally been investigated by experimental methods, while powerful computational techniques such as ISPH are gradually being adopted for such studies. This research provides further details about the application of ISPH in this area. Two projection methods to enforce incompressibility of SPH were compared from mathematical and numerical view points. Further, two pressure formulations for approximating the left-hand-side of the Poisson equation resulted in a similar trend

Report: The assessment of hospital waste management:a case study in Tehran.

Hospital waste management is an important process that must be dealt with diligently. The management of hazardous waste material requires specific knowledge and regulations and it must be carried out by specialists in the field. In this cross-sectional study, we assessed the main stages of hospital waste management including separation, containment, removal and disposal of waste materials in public hospitals affiliated with Tehran University of Medical Sciences (TUMS). We selected 108 units of six hospitals (three general hospitals and three subspecialty hospitals) from those hospitals supervised by TUMS using the cluster sampling method. The measurement was conducted through a questionnaire and direct observation by researchers. Association analysis was done by statistical tests; Fisher exact test and chi-squared using SPSS software. According to the results obtained by the questionnaire, most of the studied wards scored moderately in terms of quality of their performance in all stages of waste management. About one-fifth of the wards were suffering from poor management of their medical waste and only a minority of wards obtained good scores for managing their waste materials. The findings also revealed significant associations between temporary waste storage and collection and the level of education of the managers (P = 0.040, P = 0.050, respectively). In summary, the study indicated a moderate management in all processes of separation, collection, containment, removal and disposal of waste materials in hospitals with several observed problems in the process